Signs of approaching spring in southeast Minnesota include longer days, the return of robins — and seeing people taking ice measurements out on frozen Lake Pepin.

That annual tradition will resume next week. Each February, the U.S. Army Corps of Engineers starts sending crews out onto the frozen Mississippi River.

“We’ll take an airboat, and it’s usually a crew of about two people, and we’re drilling holes about every mile. Then it’s just measuring that ice and reporting that to our industry partners,” said Patrick Moes, deputy public affairs chief with the U.S. Army Corps of Engineers’ St. Paul District. 

They use an auger to drill a hole through the ice, and check the thickness with a measuring tape.

Shipping companies use the measurements to plan for when towboats and barges will be able to start breaking their way through the ice to begin the commercial navigation season to and from the Twin Cities.

That happens once the ice is about a foot thick. 

Lake Pepin, on the Minnesota-Wisconsin border, is wider than other nearby stretches of the Mississippi River. Because of that, it’s cloaked in a thick sheet of ice each winter — and in late winter and early spring, it’s the last frozen obstacle preventing barges full of grain, fertilizer, limestone and other goods from leaving or reaching the Twin Cities.

That makes the ice measurement information especially useful for gauging when the season will begin.

Breaking the ice

Moes said the crews measure two kinds of ice: white and blue. There’s more white ice when the weather warms up. It’s full of air, softer and easier to break. Blue ice, on the other hand, is clear and hard. 

As of the end of January, Lee Nelson — president of Upper River Services in St. Paul — estimated Lake Pepin’s ice at less than two feet thick. His firm works with shipping companies, helping towboats and barges unload their cargo, refuel and turn around. Nelson calls his company a “valet for boats.”

Some years the ice has been far thicker. Last year, it was so thin that the Corps didn’t need to measure it at all; that was an anomaly.

Once the new ice measurements are taken this month, and there are signs the ice sheet is starting to deteriorate, breaking the ice to begin the navigation season is straightforward. Contrary to their name, towboats push massive barges that carry cargo in front of them. They push the barges onto the ice, and it shatters under their weight.

Navigation season often begins around the third week of March. Until the measurements are taken, Moes said it’s difficult to predict how thick the Lake Pepin ice is this year and when it will be ready to break.

“Because of the most recent polar vortex, we’ll probably encounter some deeper ice thickness than we’ve maybe seen historically on that first ice measurement,” Moes said. “It’s hard to say. You’re always at the mercy of Mother Nature.”

Collected from Minnesota Public Radio News. View original source here.